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javascript-typescript-jest

Best practices for writing JavaScript/TypeScript tests using Jest, including mocking strategies, test structure, and common patterns.

jcasnellie69/homelab-config
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Test Structure

  • Name test files with .test.ts or .test.js suffix
  • Place test files next to the code they test or in a dedicated __tests__ directory
  • Use descriptive test names that explain the expected behavior
  • Use nested describe blocks to organize related tests
  • Follow the pattern: describe('Component/Function/Class', () => { it('should do something', () => {}) })

Effective Mocking

  • Mock external dependencies (APIs, databases, etc.) to isolate your tests
  • Use jest.mock() for module-level mocks
  • Use jest.spyOn() for specific function mocks
  • Use mockImplementation() or mockReturnValue() to define mock behavior
  • Reset mocks between tests with jest.resetAllMocks() in afterEach

Testing Async Code

  • Always return promises or use async/await syntax in tests
  • Use resolves/rejects matchers for promises
  • Set appropriate timeouts for slow tests with jest.setTimeout()

Snapshot Testing

  • Use snapshot tests for UI components or complex objects that change infrequently
  • Keep snapshots small and focused
  • Review snapshot changes carefully before committing

Testing React Components

  • Use React Testing Library over Enzyme for testing components
  • Test user behavior and component accessibility
  • Query elements by accessibility roles, labels, or text content
  • Use userEvent over fireEvent for more realistic user interactions

Common Jest Matchers

  • Basic: expect(value).toBe(expected), expect(value).toEqual(expected)
  • Truthiness: expect(value).toBeTruthy(), expect(value).toBeFalsy()
  • Numbers: expect(value).toBeGreaterThan(3), expect(value).toBeLessThanOrEqual(3)
  • Strings: expect(value).toMatch(/pattern/), expect(value).toContain('substring')
  • Arrays: expect(array).toContain(item), expect(array).toHaveLength(3)
  • Objects: expect(object).toHaveProperty('key', value)
  • Exceptions: expect(fn).toThrow(), expect(fn).toThrow(Error)
  • Mock functions: expect(mockFn).toHaveBeenCalled(), expect(mockFn).toHaveBeenCalledWith(arg1, arg2)

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accessibility

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Primary accessibility skill for VS Code. REQUIRED for new feature and contribution work, and also applies to updates of existing UI. Covers accessibility help dialogs, accessible views, verbosity settings, signals, ARIA announcements, keyboard navigation, and ARIA labels/roles.

日本語の概要は準備中です。原文の説明を表示しています。

jcasnellie69/homelab-config22026年10月11日 更新

acquire-codebase-knowledge

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Use this skill when the user explicitly asks to map, document, or onboard into an existing codebase. Trigger for prompts like "map this codebase", "document this architecture", "onboard me to this repo", or "create codebase docs". Do not trigger for routine feature implementation, bug fixes, or narrow code edits unless the user asks for repository-level discovery.

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jcasnellie69/homelab-config22026年10月11日 更新

act-on-feedback

無料

Act on user feedback attached to the current session. Use when the user submits feedback on the session's changes via the Submit Feedback button.

日本語の概要は準備中です。原文の説明を表示しています。

jcasnellie69/homelab-config22026年10月11日 更新

add-educational-comments

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Add educational comments to the file specified, or prompt asking for file to comment if one is not provided.

日本語の概要は準備中です。原文の説明を表示しています。

jcasnellie69/homelab-config22026年10月11日 更新

add-policy

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Use when adding, modifying, or reviewing VS Code configuration policies. Covers the full policy lifecycle from registration to export to platform-specific artifacts. Run on ANY change that adds a `policy:` field to a configuration property.

日本語の概要は準備中です。原文の説明を表示しています。

jcasnellie69/homelab-config22026年10月11日 更新

agent-governance

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Patterns and techniques for adding governance, safety, and trust controls to AI agent systems. Use this skill when: - Building AI agents that call external tools (APIs, databases, file systems) - Implementing policy-based access controls for agent tool usage - Adding semantic intent classification to detect dangerous prompts - Creating trust scoring systems for multi-agent workflows - Building audit trails for agent actions and decisions - Enforcing rate limits, content filters, or tool restrictions on agents - Working with any agent framework (PydanticAI, CrewAI, OpenAI Agents, LangChain, AutoGen)

日本語の概要は準備中です。原文の説明を表示しています。

jcasnellie69/homelab-config22026年10月11日 更新

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